Crop growers struggle to control volunteer plants that express a gene imparting glyphosate tolerance/glyphosate resistance in fields of glyphosate-resistant crop plants. Glyphosate is a popular and effective herbicide that is an inhibitor of 5-enolpyruvylshikimate-3-phosphate synthase. One disadvantage of glyphosate is that it can cause crop injury if applied after the crop plants are planted.
By using recombinant DNA technology, Monsanto Company (St. Louis, Mo.) has developed glyphosate-resistant crop plants, such as soybeans, corn, cotton, wheat, canola, sugarbeet, rice and lettuce. Cultivating glyphosate-resistant crops allows growers to apply glyphosate to the crop growing areas after the crop plants are planted without risking crop injury.
One issue that has emerged as a result of this technology is that due to crop rotation, glyphosate-resistant seeds from the previous season can germinate and contaminate the field the following season. For example, glyphosate-resistant corn seeds that fall to the ground during harvest may remain dormant over the winter and then germinate the following spring after crop growers have planted a different crop plant, such as soybeans, in the same field. Corn plants/weeds, or “volunteer” corn, that grow in the soybean field cannot be controlled with glyphosate treatments (such as RoundUp®, available from Monsanto Company, RoundUp is a registered trademark of Monsanto Technology LLC).
The volunteer crops cause the same problems that non-genetically modified weeds do they steal valuable resources from the crop plants. By reducing the available sunlight, soil nutrients, and moisture, the volunteer crops/weeds can drastically reduce crop yields.
Another class of herbicides, “PPO inhibitors,” work by inhibiting protoporphyrinogen oxidase (“PPO”). PPO is an enzyme that oxidizes protoporphyrinogen which disrupts the chlorophyll synthesis pathway thereby reducing photosynthesis. PPO inhibitors typically are not effective against grasses after they have germinated.
Accordingly, there is a need in the art for new methods for controlling volunteer corn that is resistant to glyphosate. The methods should have a low risk of allowing the glyphosate-resistant corn to become resistant to other chemistries. The methods should also not be phytotoxic to the crop plants or cause reductions in crop yields.